Shortness of breath during 3rd trimester?

I'm 35 weeks and over the past 3 weeks I get very short of breath and my heart races. Usually happens when I'm lying down. (especially on my left side) I have to just sit or take off my clothes because I feel like I'm hot or suffocating. Or idk if it because I get anxiety from not being able go breathe. But normally during the day I feel fine. I wanted to know if anyone else experienced this and what you did, if anything? Or is this normal during your 3rd trimester? I dont remember having this with my last two pregnancies.